This invention relates to a heat recovery system and, more particularly, to such a system in which heat is recovered from hot gases passing from a heat generator to a discharge stack.
In power plants, chemical plants, oil refineries, and the like, a relatively high volume of hot exhaust gases are formed as the exhaust products of associated equipment, such as fired heaters, boilers, gas turbines, diesel engines, furnaces, and the like. Since these gases are at a very high temperature, various type of systems have been devised to remove the heat from the gases before they are discharged to atmosphere. These systems are commonly referred to as waste heat recovery systems and are usually in the form of heaters or boilers which utilize the heat from the gases to produce saturated or superheated steam, or to heat water, air, gas, glycol, oil and other fluids.
In these systems, a waste heat recovery unit is connected to a conduit connecting the hot gas outlet of the heat generator to a discharge stack for discharging the gases into the atmosphere. The hot gases are usually drawn through the conduit, and therefore the heat recovery unit, by a fan, and the heat recovery unit includes a plurality of tubes which passes and external fluid in a heat exchange relation with the hot gases.
However, in these types of arrangements, severe problems are encountered when it becomes impossible to draw the hot gases through the conduit due to failure of the fan or the heat recovery unit, for example, since it is extremely important that the hot gases be accommodated and thus avoid shut-down of the heat generator. It has been suggested to provide a bypass conduit connecting the heat generator to the discharge stack, and an operator controlled damper in the bypass conduit at the main entrance to the discharge stack. However, this arrangement is not without problems since the damper requires operator control which often results in delays in opening, and is subject to failure due to its continuous exposure to the hot gases. The use of a bypass conduit without a damper creates another problem during normal operation of the system, since the flow of gases through the discharge stack tends to pull the relatively hot gases from the heat generator directly through the bypass conduit and into the stack without recovering the heat from the gases.